Abstract
We aimed to investigate the differences in peri-prosthetic bone remodelling between the full hydroxyapatite (HA)-collared compaction short stem and the short tapered-wedge stem. This retrospective cohort study enrolled 159 consecutive patients (159 joints) undergoing total hip arthroplasty (THA) using the full HA compaction short (n = 64) and short tapered-wedge (n = 95) stems. Body mass index (BMI), peri-prosthetic bone mineral density (BMD), and clinical factors, including the Japanese Orthopaedic Association score and the University of California Los Angeles (UCLA) activity score were assessed and compared. Stem related complications were seen in three cases. Both groups showed similar peri-prosthetic BMD changes. Peri-prosthetic BMD was almost maintained in the distal femur and Gruen zone 6 with both type of stems, but significant BMD loss was found in zones 1 and 7 in both groups and in zone 2 of the full HA compaction stem group. No significant correlations were found between the proximal femoral BMD changes and the age, BMI, and UCLA score in both the full HA compaction and tapered-wedge stem groups. Femoral bone shape affected the peri-prosthetic BMD changes in the tapered-wedge stem group but not in the full HA compaction group. The stem collar of the full HA compaction stem did not affect peri-prosthetic BMD, but unique bone remodelling in the calcar region was observed in 27.6% cases. A significant difference in the peri-prosthetic BMD changes at Gruen zone 2 was found in patients with or without thigh pain. Peri-prosthetic bone remodelling remained unaffected by clinical and radiographic factors after THA with the new short full HA compaction stem. Therefore, this new stem may be useful in a variety of cases.
Highlights
Load bearing of the peri-prosthetic bone after total hip arthroplasty (THA) is critical to maintain bone strength [1]
Stress shielding in the femur often occurs in the calcar region because it is highly unlikely that the loading of and stress distribution in the proximal femur will ever be replicated in the presence of an intramedullary prosthesis [3, 4], and the decreased bone mineral density (BMD) may lead to aseptic loosening, stem subsidence, and peri-prosthetic fractures [3, 5]
The peri-prosthetic BMD loss observed with the full HA compaction short stem was almost maintained in the middle and distal femur, that is, in Gruen zones 3, 4, 5, and 6, but significant BMD loss was found in Gruen zones 1, 2, and 7 at 24 months postoperatively, and the change in BMD was comparable to that seen with the short-tapered stem, except in Gruen zone 2
Summary
Load bearing of the peri-prosthetic bone after total hip arthroplasty (THA) is critical to maintain bone strength [1]. Stress shielding in the femur often occurs in the calcar region because it is highly unlikely that the loading of and stress distribution in the proximal femur will ever be replicated in the presence of an intramedullary prosthesis [3, 4], and the decreased BMD may lead to aseptic loosening, stem subsidence, and peri-prosthetic fractures [3, 5]. Hydroxyapatite (HA) is widely used in THA to improve implant survivorship through accelerated early bone remodelling [7, 8]. This bioactive coating is believed to enhance the initial fixation by osseointegration [7, 8]. The cancellous bone is maintained without the implant contacting to the femoral cortex, and the HA-coated femoral stem is inserted into a compacted sleeve of cancellous bone
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